Rolling bearings are assembled in vehicles and mechanical apparatuses to support the rotating parts thereof. Examples of rolling bearings include cylindrical roller bearings using cylindrical rollers, and needle roller bearings using needles as rolling bodies.
FIG. 1 illustrates a cylindrical roller bearing 1 as a rolling bearing. The cylindrical roller bearing 1 includes an outer ring 3 having an outer-ring raceway 2 around the inner-circumferential surface thereof, an inner ring 5 having an inner-ring raceway 4 around the outer-circumferential surface thereof, and a plurality of cylindrical rollers 6, each being a cylindrical rolling body, arranged between the outer-ring raceway 2 and the inner-ring raceway 4 so as to be able to roll freely. The outer ring 3 has inward-facing flange sections 7 that project inward in the radial direction on both side sections in the axial direction. The inner ring 5 has an outward-facing flange section 8 that projects outward in the radial direction on one side section in the axial direction (right side in FIG. 1). The cylindrical rollers 6 are held in pockets 10 that are formed at a plurality of locations uniformly spaced in the circumferential direction of a retainer 9 so as to be able to roll freely. In this state, the cylindrical rollers 6 are arranged such that the outside section in the radial direction of one end surface in the axial direction closely faces or comes in sliding contact with the inside surface of the inward-facing flange section 7 on one side in the axial direction and the inside surface of the outward-facing flange section 8, and the outside section in the radial direction of the other end surface in the axial direction closely faces or comes in sliding contact with the inward-facing flange section 7 on the other side in the axial direction.
FIG. 2 illustrates a cylindrical roller 6 of the cylindrical roller bearing 1. The cylindrical roller 6 is made of metal such as bearing steel or the like, and is configured as a whole in a solid cylindrical shape. The cylindrical roller 6 includes a cylindrical surface shaped rolling surface 11 as an outer circumferential surface, circular flat surfaces 12 as both end surfaces in the axial direction orthogonal to the central axis of the cylindrical roller 6, and chamfered sections 13 having an arc-shaped cross section connecting the rolling surface 11 and the flat surfaces 12.
FIG. 3 and FIG. 4 illustrate a needle roller bearing 14 as a rolling bearing. The needle roller bearing 14 includes an outer ring 3a having an outer-ring raceway 2a around the inner-circumferential surface thereof, and a plurality of needles 15, each being a cylindrical rolling body. The needles 15 are held in pockets 10a formed at a plurality of locations uniformly spaced in the circumferential direction of a retainer 9a, and in this state, are arranged between the outer-ring raceway 2a and an inner-ring raceway that is formed around the outer-circumferential surface of a shaft member (not illustrated in the figure).
FIG. 5 illustrates a needle 15 of the needle roller bearing 14. The needle 15 is made of metal such as bearing steel or the like, and similar to the cylindrical roller 6 illustrated in FIG. 2, the needle 15 is configured as a whole in a solid cylindrical shape. In other words, the needle 15 includes a cylindrical-surface shaped rolling surface 11a as an outer-circumferential surface, are circular flat surfaces 12a as both end surfaces in the axial direction that are orthogonal to the center axis of the needle 15, and chamfered sections 13a having an arc-shaped cross section connecting the rolling surface 11a and the flat surfaces 12a. The needle 15 is such that the ratio of the axial dimension with respect to the diameter is larger than the cylindrical roller 6.
Manufacturing a cylindrical rolling body such as the cylindrical roller 6 and needle 15 is generally performed as disclosed in JP-S63-278629A by a process in which an intermediate material is compression molded between a pair of molds, then in a later process, the excess material that is generated in a portion in the axial direction of the outside part in the radial direction during compression molding is removed from the intermediate material after compression molding, and finally the outer-circumferential surface and the end surfaces and the like are finished to form the rolling surface and flat surfaces.
More specifically, when manufacturing a cylindrical rolling body, for example, the molding device 16 illustrated in FIG. 6A and FIG. 6B is used. The molding device 16 includes a stationary-side mold 17 and a movable-side mold 18 that correspond to the pair of molds. The stationary-side mold 17 and the movable-side mold 18 have bottomed cylindrical-shaped molding concave sections 19 that open to one side surfaces in the axial direction facing each other. The inner surface of each of the molding concave sections 19 includes an inner-circumferential surface 20, a bottom surface 21, and an annular-shaped corner R section 22 having an arc shape cross section that connects the inner-circumferential surface 20 and the bottom surface 21.
As illustrated in FIG. 6A, a solid cylindrical-shaped intermediate material 23 is set between the stationary-side mold 17 and the movable-side mold 18. In this state, as illustrated in FIG. 6B, the intermediate material 23 is compression molded by moving the movable-side mold 18 in the axial direction toward the stationary-side mold 17, and as illustrated in FIG. 6B an intermediate material 23a is obtained.
The intermediate material 23 has a larger axial dimension and a smaller outer-diameter dimension than the completed cylindrical rolling body. Particularly, the outer-diameter dimension of the intermediate material 23 is larger than the inner-diameter dimension of the corner R section 22 (diameter dimension of the bottom surface 21) and smaller than the outer-diameter dimension of the corner R section 22 (inner-diameter dimension of the inner-circumferential surface 20). Therefore, as illustrated in FIG. 6A, in a state in which the intermediate material 23 is set between the stationary-side mold 17 and the movable-side mold 18, the outer-circumferential edges of the both end edge sections in the axial direction of the intermediate material 23 come in contact first with the respective corner R sections 22.
From this state, as the intermediate material 23 is compressed by axially moving the movable-side mold 18 toward the stationary-side mold 17, the material of the intermediate material 23 begins to flow from the vicinity of the corner R sections 22 and recesses 24 are formed in the central sections of the both end surfaces in the axial direction of the intermediate material 23. Then, from the stage in which the outside sections in the radial direction of the both end surfaces in the axial direction of the intermediate material 23 come in contact with the corner R sections 22 and the bottom surfaces 21 to some extent, the recesses 24 in the central sections of the both end surfaces in the axial direction of the intermediate material 23 remain, and in this state, compression molding of the intermediate material 23 preferentially proceeds in a direction in which the outer-diameter dimension becomes larger. At this time, a part of the material of the intermediate material 23 bulges into a gap 25 between the stationary-side mold 17 and the movable-side mold 18. As a result, as illustrated in FIG. 6B, in the intermediate material 23a after the compression molding, the recesses 24 in the both end surfaces in the axial direction remain, and excess material 26 is formed on the outside section in the radial direction of the middle section in the axial direction. In this way, since the material of the intermediate material 23 immediately fills the inner-circumferential surfaces 20 of the molding concave sections 19, the excess material 26 bulges into the gap 25 before the material is sufficiently filled toward the bottom surfaces 21 of the molding concave sections 19.
After the compression molding, the intermediate material 23a is removed from between the stationary-side mold 17 and the movable-side mold 18, after which, in a post process, finishing such as flattening the both end surfaces in the axial direction, including removing the excess material 26 and removing the recesses 24, smoothing the outer-circumferential surface, and the like is performed, whereby the shape and dimensions required for the cylindrical rolling body are given.
In this way, in the manufacturing of a conventional cylindrical rolling body, it is required to remove the excess material 26 and remove the recesses 24 in a post process. However, in the case of removing the excess material 26 by forging in a post process, handling the scrap material is difficult. For example, there is a possibility that scraps will remain without being properly discharged from the mold, and will be engulfed and molded into the next product. Moreover, in a post process, in the case of performing a process that includes removing the excess material 26 and removing the recesses 24 by grinding, there is a problem in that the processing expense is large, processing requires a long time, and the manufacturing cost becomes high.
In JP2007-083259A, a technique of a method for manufacturing a cylindrical rolling body is disclosed in which, by performing compression molding of an intermediate material after first forming holes with bottoms in the both end surfaces in the axial direction of the intermediate material, excess material escapes into the inner-circumferential surfaces of the holes with bottoms, and prevents excess material from bulging into the outside section in the radial direction. However, with this conventional technique, it is inevitable that the holes with bottoms will remain in the both end surfaces in the axial direction of the completed cylindrical rolling body. Therefore, this conventional technique cannot be adopted in the case where the cylindrical rolling body to be manufactured is of a solid structure having no holes with bottoms in the both end surfaces in the axial direction.